The New Sudoku Players' Forum

[ronk]

With puzzle #741 of the top1465 ...

Code: Select all

 *-----------*
 |.3.|.6.|...|
 |..4|.5.|..7|
 |.5.|7..|.8.|
 |---+---+---|
 |...|..1|...|
 |...|...|7..|
 |3..|...|465|
 |---+---+---|
 |.1.|..7|..4|
 |..5|81.|...|
 |.7.|...|29.|
 *-----------*

... I get to this "sticking point" ...

Code: Select all

 *-----------------------------------------------------------*
 | 17    3     27    | 12    6     8     | 5     4     9     |
 | 8     69    4     | 19    5     3     | 16    2     7     |
 |*129   5     269   | 7    ^29    4     | 136   8     36    |
 |-------------------+-------------------+-------------------|
 | 2457  246   267   | 45    48    1     | 9     3     28    |
 | 2459  249   29    | 345   348   6     | 7     1     28    |
 | 3     8     1     | 29    7     29    | 4     6     5     |
 |-------------------+-------------------+-------------------|
 |^29    1     3     | 6    ^29    7     | 8     5     4     |
 | 249   249   5     | 8     1     29    | 36    7     36    |
 | 6     7     8     | 34    34    5     | 2     9     1     |
 *-----------------------------------------------------------*

... and using the uniqueness principle based on the 29 rectangle at r37c15, try to make the placement r3c1=1. Simple Sudoku (SS) rejects it. During reload of the puzzle, I verified that SS does not report multiple solutions.

What am I missing? Are there multiple solutions which SS does not catch? Or does some other "uniqueness pattern" have precedence over this one?

TIA, Ron

[Jeff]

What am I missing? Are there multiple solutions which SS does not catch? Or does some other "uniqueness pattern" have precedence over this one?

That's not a valid unique rectangle,Ronk.

[vidarino]

Hmm, that's not a Uniqueness Rectangle (type 1), if that's the reason you're setting R3C1=1. URs need two pairs of corners that share the same box.

Also, the 9 in R3C1 can be eliminated with an XYZ-wing in R3C3, R2C2 and R3C5;
R3C5=2 -> R3C3+R2C2 = naked pair 69 -> elim 9 from R3C1
R3C5=9 -> elim 9 from R3C1

Other than that, the puzzle definitely has a unique solution, and there *is* actually a real Unique Rectangle there; Look in R38C79 for the real one.

[ronk]

That's not a valid unique rectangle,Ronk.

I had figured that out by using another solver, so that's like hearing grass isn't purple, Jeff

[ronk]

Hmm, that's not a Uniqueness Rectangle (type 1), if that's the reason you're setting R3C1=1. URs need two pairs of corners that share the same box.

So the Unique Rectangle (type 1) exists only if the rectangle is wholly within one tower or one floor. Got it, thanks.

Also, the 9 in R3C1 can be eliminated with an XYZ-wing in R3C3, R2C2 and R3C5

I've never found an xyz-wing on my own yet. Never will either if I don't start looking for them.

there *is* actually a real Unique Rectangle there; Look in R38C79 for the real one.

I see it now.

Thanks again, Ron

[Jeff]

I had figured that out by using another solver, so that's like hearing grass isn't purple, Jeff

Sorry Ronk, Just don't know how I should explain that to you apart from informing that the unique rectangle was incorrectly picked.

[QBasicMac]

Sorry Ronk, Just don't know how I should explain that to you apart from informing that the unique rectangle was incorrectly picked.

Speaking for myself, I get annoyed at cryptic quickie replies. Maybe ronk did the same.

You could have said a few more words, like why it is not valid, thereby avoiding an ill-humored response.

Mac

[Jeff]

You are quite right, Mac. Thanks for the advice.